1. Field of the Invention
The present invention relates to a method for enhancing the separation of oil and water dispersions and emulsions. More particularly, the present invention is concerned with enhancing separation of oil and water emulsions and dispersions by treating the same with microwave radiation, whether alone or in conjunction with more conventional separating devices.
In the petroleum industry, most of the crude oil produced is co-mingled with water and gas. It is therefore necessary to provide a means of sufficiently and economically separating the oil, gas and water for separate discharge. Usually the separated water is returned to a subterranean formation containing oil and the separated oil is conducted to a pipeline for ultimate transportation to a refinery and end use. Normally, the separated gas is vented if in small quantities or if in commercial quantities collected for distribution and sale.
Primary production of oil from subterranean oil-bearing reservoirs is normally obtained by exploiting the natural drive energy of the reservoir in the form of water drive, gas cap drive, solution gas drive, and combinations thereof. Oil remaining in the reservoir after primary energy sources have been depleted can be partially recovered by secondary recovery methods. One of the most common secondary recovery methods is waterflooding. Using this method, flooding water is injected into the reservoir through one or more injection wells penetrating the oil-bearing reservoir. The water displaces the oil in the reservoir and moves it through the reservoir toward one or more production wells from which oil is produced. Produced oil, whether from natural drive, secondary recovery or enhanced oil recovery operations, often contains water which must be separated from the produced oil.
With the rising value of petroleum products, it becomes increasingly important that separator equipment utilized by the petroleum industry extract the maximum possible recovered petroleum products from oil and water emulsions and dispersions. To this end, improved separating vessels have been developed over the years. Initially, the separators were merely open vessels providing a quiet zone with the intention that the water settle out and be withdrawn from the bottom of the vessel and that the petroleum float on the water and be withdrawn from the top of the vessel. While this system is satisfactory to a degree, it nevertheless results in some oil remaining in the form of an emulsion or dispersion with the withdrawn water, and in like manner in water being entrapped with the oil withdrawn from the top of the vessel. Further, such gravitational settling procedures are slow and require vessels of such volume that to allow separation by gravitation alone becomes excessively expensive, and the slow separation rate results in general overall inefficiency.
2. The Prior Art
Representative but non-exhaustive examples of various types of apparatus previously used in the art of separating co-produced oil and water are gun barrel treaters, heater treaters, and the like. An apparatus specifically designed for use in separating oil and water can be found in, for example, U.S. Pat. No. 4,257,895. The use of ultrasonics is known for breaking oil-water emulsions as described in U.S. Pat. Nos. 2,257,997; 3,200,567; and 3,594,314. Other references disclose the application of microwave energy in the recovery of oil from oil wells and oil shale, including U.S. Pat. Nos. 3,104,711, 3,133,592; 3,170,519 and 4,180,718. Microwave energy has also been used in settling of solids and sewage and sewage sludge, such as described in U.S. Pat. No. 3,523,076. The use of a fibrous coalescer to aid in separation of an emulsion is described in U.S. Pat. No. 2,494,392.
More recently, a method for enhancing the separation of oil and water from an emulsion or dispersion was described in U.S. Pat. No. 4,582,629. The method described in that patent has been effective up to a point, but has been limited in application because of certain energy inefficiencies. The present invention provides a system for improving the efficiency of microwave-based oil-water separators.
It is accordingly an object of this invention to provide a microwave based oil-water separation system having a higher efficiency than previously available systems.